Various photosensitive compositions have been used in the manufacturing process of a lithographic printing plate, a semiconductor such as IC, in production of circuit boards for a liquid crystal device and a thermal head, and in the process of photofabrication for other devices. As the photosensitive compositions for these uses, photoresist photosensitive compositions are generally utilized, and they are broadly classified into two groups, namely the group of positive photoresist compositions and the group of negative ones.
Representatives of such positive photoresist compositions are chemical amplification resist compositions as disclosed in U.S. Pat. No. 4,491,628 and European Patent No. 249,139.
Chemical amplification positive resist compositions are materials for forming patterns on substrates. More specifically, these compositions generate acids by irradiation with actinic rays, such as far ultraviolet rays, and undergo reaction utilizing these acids as a catalyst. This reaction causes a difference in solubilities in a developer between the areas unirradiated and irradiated with the actinic rays, thereby enabling pattern formation.
Examples of such chemical amplification positive resist compositions include the combination of a compound capable of generating an acid by photolysis (hereinafter abbreviated as a photo-acid generator) and an acetal or O,N-acetal compound (JP-A-48-89003, the term “JP-A” as used herein means an “unexamined published Japanese Patent application), the combination of a photo-acid generator and an orthoester or amidoacetal compound (JP-A-51-120714), the combination of a photo-acid generator and a polymer having acetal or ketal groups on the main chain (JP-A-53-133429), the combination of a photo-acid generator and an enol ether compound (JP-A-55-12995), the combination of a photo-acid generator and an N-acylaminocarbonic acid compound (JP-A-55-126236), the combination of a photo-acid generator and a polymer having orthoester groups on the main chain (JP-A-56-17345), the combination of a photo-acid generator and a tertiary alkyl ester compound (JP-A-60-3625), the combination of a photo-acid generator and a silyl ester compound (JP-A-60-10247), and the combination of a photo-acid generator and a silyl ether compound (JP-A-60-121446). These compositions have high photosensitivity since the their quantum yields are each greater than 1 in principle.
As examples of a system which is stable upon storage at room temperature but decomposed by heating in the presence of an acid to become alkali-soluble, mention may be made of the systems obtained by combining tertiary or secondary carbon-containing (such as t-butyl or 2-cyclohexenyl) ester or carboxylic acid ester compounds and compounds capable of generating acids by exposure as described in JP-A-59-45439, JP-A-60-3625, JP-A-62-229242, JP-A-63-27829, JP-A-63-36240, JP-A-63-250642, Polym. Eng. Sce., vol. 23, p. 1012 (1983), ACS. Sym., vol. 242, p. 11 (1984), Semiconductor World, the November issue in 1987, p. 91, Macromolecules, vol. 21, p. 1475 (1988), and SPIE, vol. 920, p. 42 (1988). These systems also have high photosensitivity, and show poor absorption in the far ultraviolet region. Therefore, they can be effective in enabling the use of a light source with shorter wavelengths suitable for submicron photolithography.
The chemical-amplification positive resist compositions as mentioned above are broadly classified into two groups. One group includes three-component systems which are each constituted of an alkali-soluble resin, a compound capable of generating an acid upon exposure to radiation (photo-acid generator) and a compound having an acid-decomposable group and inhibiting dissolution of an alkali-soluble resin. The other group includes two-component systems which are each constituted of a resin having groups capable of being decomposed by reaction with an acid to become alkali-soluble and a photo-acid generator.
In such two-component or three-component positive resist of chemical amplification type, resist patterns are formed by development after thermal treatment in the presence of an acid generated from a photo-acid generator by exposure.
As mentioned above, such chemical amplification positive resist compositions can be systems suitable for a light source with shorter wavelengths enabling submicron photolithography. However, further improvements in resolution and process latitude, including exposure margin or focus depth, have been required for them.
In such systems, compounds capable of generating trifluoromethanesulfonic acid, such as triphenylsulfonium trifluoromethanesulfonate, and compounds capable of generating longer-chain fluoroalkylsulfonic acids are used as photo-acid generators.
Further, compounds capable of perfluoroalkanesulfonic acids, such as triphenylsulfonium triflate and bis(t-butylphenyl)iodonium perfluorobutanesulfonate, are also well known as photo-acid generators. A compound capable of generating a perfluorobutanesulfonic acid is described in WO 00/08525, JP-A-09-12537, JP-A-2000-275845 and EP 1041442A.
In general, perfluoroalkyl compounds have high hydrophobicity, so they are used for water-repellent coating on clothes. Therefore, the resist using an acid generator capable of generating a perfluoroalkylsulfonic acid upon irradiation with actinic rays has a low affinity for aqueous developers, and so it suffers from a sensitivity drop and scum development due to degradation in developability.
Further, the arts mentioned above cannot satisfactorily meet the current needs for photolithography and have room for improvements in resolution and process latitude, including exposure margin and focus depth.